This invention relates to a method of depositing dielectric on a semiconductor substrate to form part of a capacitor.
In order to reduce the size of capacitors required in semiconductor devices the industry is moving towards the use of high dielectric constant (k) materials. One Particular favoured material is Tantalum Pentoxide (Ta2O5) is a particularly promising candidate with a dielectric constant of about 25. This material can be deposited by various chemical and physical means, but the most convenient for semiconductor work is vapour deposition. This process is well known in general and is for example described in U.S. Pat. No. 5,111,355. From this it will be seen that Tantalum is one of a class of materials in which the oxide forms on the surface of the metal target and is sputtered from the target, in contrast to other reactive processes where the oxide or nitride is formed in flight or on the surface of the substrate. Possibly because of this factor problems can arise from a relatively high leakage current through the deposited layer. As will be seen in U.S. Pat. No. 5,872,696 it is thought that this is in part due to pin holes and in part due to the presence of un-oxidised Tantalum atoms within the layer linking to form a leakage path. In that Patent a reduction of the leakage current is achieved by further anodisation of the Tantalum Pentoxide. This reduces the pinholes and/or the conductive paths sufficiently to allow large area capacitors to be formed. However, with small area capacitors relatively high leakage currents (of the order of >1−6 amps when 5 volts is applied against a layer of 100 thickness of Tantalum Pentoxide).